1. Field of the Invention
This invention relates to a giant-size color image display device of a construction, in which are arranged a multitude of cathode ray tubes to form a plurality of luminescent colors.
2. Description of Prior Art
Numerous problems have been encountered with those giant-sized display devices such as, for example, lighting display board at the baseball field, information display boards used on the roof-top or the wall surfaces of buildings, highways, and so on for transmitting commercial messages and pictures, traffic information, and so forth to general public, because such conventional display devices form picture images by arranging a multitude of electric bulbs which are selectively turned on and off.
Giving a few examples from among them: in the case of using electric bulbs, since light is obtained by incandescence of the bulb filament, the light emitted from it mainly assumes orange or whitish orange in color. On account of this, it is fairly difficult to cause a large amount of colored light in, for example, blue and green to be emitted from these electric bulbs. Further, in such display device using electric bulbs, brightness in each picture element has to be modulated by turn-on or turn-off of the electric current to be applied to the bulb filament, or making variable the electric current to be applied. These electric bulbs, however, are extremely low in their frequency response, which is as low as 10 Hz or below, on account of which the luminescent color per se to be emitted from these bulbs is subjected to change depending on the applied current, and also difficulty is accompanied in providing an intermediate tone display and a color display produced by combination of arbitrary colored lights. Furthermore, in such giant-sized display device, electric bulbs of 20 W to 40 W or so have to be arranged generally in a great number ranging from a few thousands to several tens of thousands or more with the consequence that there have been problems such as higher power consumption and considerable heat generation.
In view of such circumstances with the conventional display device, the present inventor proposed use of cathode ray tubes as the light source for such display device.
That is to say, according to this proposal, a desired picture image is displayed by, for example, arranging a large number of small-sized cathode ray tubes, each having a monochromatic fluorescent face such as red, green, blue, etc. According to this technique, not only energy conversion efficiency in converting electric energy to light energy can be remarkably improved in comparison with that of the electric bulb, but also various other advantages are resulted such that light sources in arbitrary luminescent colors can be obtained by selection of fluorescent material to be used, and so forth. When the cathode ray tube is used as the light source for such giant-sized display device, the display device can apparently be constructed with more advantages in its performance, operational reliability, maintenance cost, power consumption, and so on in comparison with those of the conventional bulb type display device.
FIG. 1 of the accompanying drawing illustrates one embodiment of the cathode ray tube to be employed as the light source for the giant-sized display device which the present inventor has so far put into practice as the prior art. In the drawing, a reference numeral 1 designates a vacuum envelope to maintain the interior of the cathode ray tube in the vacuum, which is in a cylindrical shape, for example. This vacuum envelope 1 has at its one end a face glass 3 with a fluorescent layer 2 having been coated on the inner surface thereof, and has, at its other end, an electron gun 5 for irradiating the overall surface of the fluorescent layer 2 with non-converging electron beam 4, terminals 6 for applying a required electric voltage to every part of the electron gun 5, and a stem part 7 to close the vacuum envelope 1. Numerals 8, 9 and 10, respectively, refer to a heater, a cathode, and a grid, all constituting the above-mentioned electron gun 5.
Explaining further the operations of this cathode ray tube, when a negative voltage is imparted to the cathode 9 through the grid 10 and predetermined electric current is caused to flow in the heater 8, thereby heating the cathode 9 and bringing the voltage in the grid 10 closer to an electric potential in the cathode 9, electron beam 4 is emitted from the cathode 9 to the fluorescent layer 2. The electron beam 4 is irradiated over the entire surface of the fluorescent layer 2 in the form of a non-converging beam having a predetermined expansion angle .theta. depending on various conditions such as a diameter of an aperture formed at the center of the grid 10, a space gap between the grid 10 and the cathode 9, an anode voltage, and so on, thereby causing the fluorescent layer 2 to emit light in a luminescent color in accordance with the fluorescent material used. As shown, for example, in FIG. 2, the cathode ray tubes are arranged in such a regular manner that the side thereof having the fluorescent layer 2 is faced frontward, and that each one of cathode ray tube 22 to emit red light and cathode ray tube 23 to emit blue light may come in between every two cathode ray tubes 21 to emit green light.
Explaining such arrangement of the cathode ray tubes in reference, for example, to FIG. 2, when a multitude of cathode ray tubes, each having a diameter of about 29 mm, are arranged, they are disposed at a pitch of 40 to 45 mm, taking into account a problem in constructing the display device in a water-tight structure in consideration of its outdoor use, and structure and convenience in wiring of the socket portion for supplying voltage to the cathode ray tube. In this case, however, the optimum viewing distance of the display device for easiness in viewing the displayed image and from the point of degree of color mixture is approximately 70 m or longer, which distance raises no particular problem as the display device for the benefit of spectators in the baseball field, for example. It has however been found out that, when considering use of such display device for indoor installation, outdoor advertisement, and so on, this viewing distance should be reduced to a half or shorter.
As method for reducing this viewing distance to a large extent, therefore, attempts have been made in obtaining a plurality of lights in the elementary colors with a single cathode ray tube, wherein the fluorescent layer in the light source cathode ray tube constituting each picture element is split into a plurality of sections and the fluorescent layers to emit different luminescent colors are combined.
FIG. 3 illustrates one example of such cathode ray tube 31. In this embodiment, the fluorescent layer 2 is split into three sector-shaped portions with the center of the tube being made the dividing point so that the elementary color lights of red (R), green (G), and blue (B), each being in substantially sector shape, may be emitted. Such cathode ray tube 31 is constructed, as shown, for example, in FIGS. 4 and 5, with the split fluorescent layers 2a in different color of their luminescent light and the electron guns 5a to generate non-converging electron beam 4a which cause these fluorescent layers to illuminate in predetermined colors, in combination. Accordingly, the fluorescent layer 2a of FIG. 4 is provided at the forward end of the electron gun 5a, while the fluorescent layer 2a of FIG. 5 is provided on the inner surface of the face glass 3.
When a multitude of such composite type light source cathode ray tubes are arranged to construct the image display device, the viewing distance thereof was found to be reduced to a half in comparison with the conventional display device constructed by arranging the single tube, monochromatic type light source cathode ray tubes.